Читать книгу The Religion of Geology and Its Connected Sciences - Edward Hitchcock - Страница 4

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This section of the earth’s crust is intended to bring under the eye the leading features of geology.

1. The relative Position of the Stratified and the Unstratified Rocks.

The unstratified rocks, viz., granite, sienite, porphyry, trap, and lava, are represented as lying beneath the stratified class, for the most part, yet piercing through them in the centre of the section, and by several dikes or veins, through which masses have been protruded to the surface. The unstratified class are all colored red, to indicate their igneous origin. Granite seems to have been first melted and protruded, and it continued to be pushed upward till the close of the secondary period of the stratified rocks, as is shown by the vein of granite on the section. Sienite and porphyry seem to have been next thrust up, from below the granite; next, the varieties of trap were protruded from beneath the porphyry; and last, the lava, which still continues to be poured out upon the surface from beneath all the rest.

2. The Stratified Rocks.

The stratified rocks represented on both flanks of the granite peak in the section, appear to have been deposited from water, and subsequently more or less lifted up, fractured, and bent. An attempt is made, on the right hand side of the section, to exhibit the foldings and inclination of the strata. The lowest are bent the most, and their dip is the greatest; and, as a general fact, there is a gradual approach to horizontality as we rise on the scale.

3. The right hand side of the Section.

The strata on the right hand are divided into five classes: first and lowest, the crystalline, or primary, destitute of organic remains, and probably metamorphosed from a sedimentary to a crystalline state, by the action of subjacent heat. 2. The palæozoic class, or those containing the earliest types of animals and plants, and of vast thickness, mostly deposited in the ocean. 3. The secondary class, reaching from the top of the lower new red or Permian system, to the top of the chalk. 4. The tertiary strata, partially consolidated, and differing entirely from the rocks below by their organic contents. 5. Alluvium, or strata now in a course of deposition. This classification is sometimes convenient, and frequently used by geologists.

4. The left hand Side.

On the left hand side of the section the strata are so divided as to correspond to the six great groups of animals and plants that have appeared on the globe. The names attached to the groups are derived from ζωὁς (vivus, living,) with the Greek numerals prefixed. The lowest group, being destitute of organic remains, is called azoic, (from α privitive and ζωὁς,) that is, wanting in the traces of life; and corresponds to the crystalline group on the other side of the section, embracing gneiss, mica slate, limestone, and clay slate, of unknown thickness. The protozoic group corresponds to the palæozoic of the right hand side, and embraces lower and upper Silurian, Devonian, or old red sandstone, the carboniferous group, and the Permian, or lower new red; the whole in Great Britain not less than thirty-three thousand feet thick. The deutozoic group consists only of the triassic, or upper new red sandstone, and is only nine hundred feet thick, but marks a distinct period of life. The tritozoic embraces the lias and oölite, with the Wealden, and is three thousand six hundred feet thick. The tetrazoic consists of the chalk and green sand, one thousand five hundred feet thick. The pentezoic embraces the tertiary strata of the thickness of two thousand feet. The hectozoic is confined to the modern deposits, only a few hundred feet thick, but entombing all the existing species of animals.

5. Characteristic Organic Remains.

Had space permitted, I should have put upon the section a reference to the most characteristic and peculiar mineral, animal, or plant, in the different groups. Thus the azoic group is crystalliferous, or crystal-bearing. The lower or Silurian part of the protozoic group is brachiopodiferous, trilobiferous, polypiferous, and cephalopodiferous; that is, abounding in brachiopod and cephalopod shells; in polypifers, or corals; and in trilobites, a family of crustaceans. The middle part, or the Devonian, is thaumichthiferous, or containing remarkable fish. The upper part, or the coal measures, is carboniferous; that is, abounding in coal. The deutozoic group is ichniferous, or track-bearing, from the multitude of its fossil footmarks. The tritozoic group is reptiliferous, or reptile-bearing, from the extraordinary lizards which abound in it. The tetrazoic is foraminiferous, from the abundance of coral animalcula, called foraminifera, or polythalmia, which it contains. The pentezoic is mammaliferous, because it contains the remains of mammalia, or quadrupeds. The hectozoic is homoniferous, or man-bearing, because it embraces human remains.

There is no one place on earth where all the facts exhibited on this section are presented before us together. Yet all the facts occur somewhere, and this section merely brings them into systematic arrangement.